[chromium] Add WebUnitTestSupport::createLayerTreeViewForTesting for webkit_unit_tests
https://bugs.webkit.org/show_bug.cgi?id=109403

Reviewed by Adam Barth.

Source/Platform:

webkit_unit_tests that need compositing support need only a simple WebLayerTreeView implementation, not the full
thing.

* chromium/public/WebCompositorSupport.h:
(WebCompositorSupport):
(WebKit::WebCompositorSupport::createLayerTreeView):
* chromium/public/WebUnitTestSupport.h:
(WebKit):
(WebUnitTestSupport):
(WebKit::WebUnitTestSupport::createLayerTreeViewForTesting):

Source/WebKit/chromium:

* tests/GraphicsLayerChromiumTest.cpp:
(WebKit::GraphicsLayerChromiumTest::GraphicsLayerChromiumTest):
* tests/ScrollingCoordinatorChromiumTest.cpp:
(WebKit::FakeWebViewClient::initializeLayerTreeView):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@142568 268f45cc-cd09-0410-ab3c-d52691b4dbfc